RESEARCH ARTICLE

Perceived Fatigue for Short- and Long-Haul Flights:

A Survey of 739 Airline Pilots

Samira Bourgeois-Bougrine, Philippe Carbon,

Charlotte Gounelle, Regis Mollard, and Alex Coblentz

BOURGEOIS-BOUGRINE S, CABON P, GOUNELLE C, MOLLARD R,

COBLENTZ A. Perceived fatigue for short- and long-haul flights: a

survey of 739 airline pilots. Aviat Space Environ Med 2003; 74:

1072–7.

Background: Fatigue-related incidents in aviation may be self-reported by pilots in confidential systems. The aim of this study was to

clarify what fatigue means to pilots on short- and long-haul flights (SHF

and LHF, respectively). Methods: Questionnaires were distributed to

pilots through four airlines. Questions concerned the perceived causes

of fatigue, its signs and symptoms in the reporting pilot and observed in

others, as well as the strategies used to minimize its impact. Results: Of

3,436 questionnaires distributed, 739 (21.5%) were returned. For LHF,

fatigue was seen as mainly due to night flights (59%) and jet lag (45%).

For SHF, fatigue was caused by prolonged duty periods (multi-segment

flights over a sequence of 4 to 5 d) (53%) and successive early wake-ups

(41%). Self-reported manifestations of fatigue in 60% of LHF pilots and

49% of SHF pilots included reduction in alertness and attention, and a

lack of concentration. Signs observed in other crewmembers included

an increase in response times and small mistakes (calculation, interpretation). When pilots were tired, all the flying tasks seemed to be more

difficult than usual. In both LHF and SHF, rest and sleep management

were the primary strategies used to cope with fatigue. Analysis showed

that duty time is a major predictor of fatigue, but that it cannot be

considered independently from the other contributory factors. Conclusion: For both LHF and SHF, pilots reported acute fatigue related to sleep

deprivation, due mainly to work schedules: night flights, jet-lag, and

successive early wake-ups. These causal factors could easily be assessed

in investigation of accidents and incidents.

Keywords: fatigue, sleep loss, long duty time, work schedules, accident

and incident investigation, civil aviation, long-haul flights, short-haul

flights.

FATIGUE IS recognized as one of the major factors

that can impair human performance, and has often

been cited as a cause of accidents and incidents in

industry and transport (11). The evidence of a causal

influence of fatigue in incidents or accidents is often

circumstantial because fatigue is a complex and ambiguous concept with no standard measurement index (2).

For example, Lyman and Orlady (10) showed that fatigue was implicated in 77 (3.8%) of 2,006 incidents

reported by pilots to the Aviation Safety Reporting

System (ASRS). When the analysis was expanded to

include all factors that could be directly or indirectly

linked to fatigue, incidents potentially related to fatigue

increased to 426 (21.2%). The major problem with fatigue issues is the lack of a coherent definition of fatigue

itself, and of a reliable and valid assessment tool to

measure it. Therefore, fatigue is generally difficult to

investigate on a systematic basis and to code into databases (5).

Studies of pilot fatigue have used various methods,

usually measuring fatigue by continuously recording

pilots’ electroencephalograms, electrooculograms, and

electromyograms during commercial flights, collecting

sleep diaries, and measuring performance on specific

tasks (3,6,13). Because of night flights and jet lag, longhaul flights (LHF) have generally received more interest

than short-haul flights (SHF) with respect to fatigue

(3,12,13,15).

As suggested in a recent symposium (11), fatigue in

aviation refers to decreases in alertness, and feeling

tired, sleepy, and/or exhausted. This concept of fatigue

is based on outcomes that are measured by electrophysiological recording during flight and is therefore difficult to use in accident and/or incident investigations.

As fatigue is an internal experience, we each possess a

personal knowledge of its causes and manifestations.

The aim of the present study was to evaluate this personal experience in order to understand pilots’ perception of fatigue in short- and long-haul flights. It is

concerned with the physiological, psychological, and

operational factors related to the causes of fatigue, with

the most striking symptoms, and finally with the strategies or countermeasures used by pilots to counteract

fatigue. This study, which is part of a larger program

examining aircrew fatigue, may help investigators to

easily identify fatigue in analysis of accidents and incidents, as well as improving our understanding of incidents self-reported by pilots to confidential and voluntary reporting systems.

METHODS

The questionnaire was developed to evaluate these

aspects and included open and closed questions and

From the Universite ́ Rene ́ Descartes-Paris 5 - Laboratoire

d’Anthropologie Applique ́e, Paris, France.

This manuscript was received for review in February 2002. It was

revised in July and November 2002, and May 2003. It was accepted for

publication in June 2003.

Address reprint requests to: Regis Mollard, Universite ́ Rene ́ Descartes-Paris 5 - Laboratoire d’Anthropologie Applique ́e, 45, rue des

Saints-Pe`res, 75006 Paris, France; laa@biomedicale.univ-paris5.fr.

Samira Bourgeois-Bougrine, Ph.D., is a lecturer in Ergonomics at

Universite ́ Paris 5.

Reprint & Copyright © by Aerospace Medical Association, Alexandria, VA.

1072 Aviation, Space, and Environmental Medicine • Vol. 74, No. 10 • October 2003
two kinds of ratings.* For the causes of fatigue, the

closed questions included a checklist of factors as well

as ratings of the impact of these factors on five-point

scales like those generally used in shift work studies (1).

For the subjective experience or manifestations of fatigue, visual analog scales were used (9). The questionnaire included five parts:

Demographic information: age, gender, flying experience, function (captain or co-pilot), and flight category

(short- or long-haul).

Level of fatigue. A visual analog scale of fatigue was

used on which pilots marked their current feeling on a

100-mm line from “fresh” (0) to “tired” (100). Information was also gathered on duty time over the previous

7 d (duty week, DW), including total duty time and the

share performed between midnight and 0600 (home

time).

Causes of fatigue (3 questions). Which of your usual

schedules make you feel tired (open question)? During

climb and descent, to what extent do the following

situations make you tired? Eight items were indicated

and the ratings were made on a 5-point scale of impact

(1  none, 2  small, 3  medium, 4  high, 5  very

high). In general, what is the impact of the following

events on your level of fatigue? Five items related to

flight changes or difficulties were rated on a five-point

scale of impact as above.

Manifestations of fatigue (2 questions). During the flight,

what are the symptoms of fatigue for you and for the

other crewmembers (open question)? When you get

tired, to what extent are the following flying tasks affected by fatigue? Performance on eleven kinds of flying tasks was rated using a 100-mm line where 0 

better than usual, 50  as usual, 100  less well than

usual.

Coping strategies. What are your strategies to cope

with fatigue before and after an exhausting roster, during flight, and during layover (open question)?

Results for LHF and SHF were compared using

Mann-Whitney U (nonparametric) tests. Differences related to age and sex were evaluated by ANOVA. Regression analyses were performed to evaluate the impact of the duty time performed over the DW

(independent variable) on the level of fatigue (dependent variable).

The aims of the survey were explained by telephone

or letter to the heads of flight divisions in five French

airlines. The questionnaires and stamped self-addressed envelopes were then provided to the airlines

and distributed to each pilot’s in-house mailbox. Pilots

were invited to participate in the survey and to return

the questionnaire anonymously to our laboratory as

soon as possible. A reminder letter was subsequently

addressed to all the pilots in the five airlines. Pilots from

one airline returned their questionnaires after the completion of the data analyses and their results were thus

excluded.

RESULTS

The four study airlines employed a total of 3,436

pilots. Of 3,436 questionnaires distributed, 739 (21.5%)

were returned. The response rate for individual airlines

ranged from 2% to 33%; 615 of the returns came from

one large airline. The sample of 739 pilots comprised

95% men and 5% women, 46% captains and 54% first

officers, 72% LHF and 28% SHF. The mean age of the

respondents was 42 8 yr (range 25 to 61), and the

mean flying experience was 14 yr (range 1 to 39). Age

and flying experience were significantly correlated (r 

0.82; p  0.001). The distribution in terms of age, sex,

and function in the sample was close to the overall

numbers for the airlines in 1997, the year of the survey,

as reported by the head of each flight division.

Fatigue and Duty Time

The mean duty time performed by the pilots during

the DW was 25 15 h (max: 80 h), and the average level

of fatigue was 51 24.5 (max: 99) on the visual analog

scale. In this survey, 90% of the SHF pilots performed

their duty time during the day, while 80% of LHF pilots

performed the whole, or the majority of their duty time

between 0 h and 6 h. However, there was no difference

between the SHF and LHF with respect to average duty

time or average level of fatigue. Simple and multiple

regression analyses were performed for SHF and LHF,

respectively, with fatigue as the dependent variable and

diurnal and nocturnal (for LHF) duty times as the independent variables. As was expected, fatigue increased significantly with duty time in both kinds of

flights (Table I). In addition, for the LHF, the standardized coefficient values indicated that nocturnal duty

was the most important in predicting fatigue. However,

the low R2 values (SHF: R2

0.23, LHF: R20.11) suggest that the majority of the variability in the level of

fatigue cannot be explained by duty time.

Causes of Fatigue

The LHF and SHF pilots reported 704 and 248 examples, respectively, of schedules that made them feel * Questionnaire available on-line at http://www.ingentaselect.

com/vl1151019/cl61/nw1/rpsv/cw/asma/00956562/contp1-1.htm.

TABLE I. RESULTS OF SIMPLE AND MULTIPLE REGRESSION ANALYSIS FOR SHF AND LHF, RESPECTIVELY.

Std Coeff (ß) t-value p-value

SHF : R  .48; R2  .23 Diurnal duty .48 4.84 0.001

LHF : R  .33; R2  .11; F  21.89, p  0.001 Diurnal duty .19 3.77 0.001

Nocturnal duty .29 5.85 0.001

The dependent variable is fatigue. Independent variables are diurnal duty time for SRH and both diurnal and nocturnal duty for LRH. (Std :

standardized; coeff : coefficient).

PILOT FATIGUE SURVEY—BOURGEOIS-BOUGRINE ET AL.

Aviation, Space, and Environmental Medicine • Vol. 74, No. 10 • October 2003 1073
tired. Among these examples, two schedules in particular were frequently reported (8%):

1. LHF: flights on two successive nights with a sleep

during a short day layover. For example: ParisNew York-Paris in 48 h with a layover of about

22 h.

2. SHF: long duty periods (more than 10 h) that

included 4 to 5 legs per day with successive early

wake-ups over a sequence of 4 d.

An analysis of the features of the 952 examples of

schedules reported by the pilots indicated that the main

causes of fatigue were related to sleep deprivation and

biological rhythm disturbances for LHF, and to daily

workload and sleep deprivation for SHF. Indeed, LHF

fatigue was mainly due to night flights (59% of roster

examples), jet lag (45%), and minimum crew (13%). SHF

fatigue was associated with schedules of 4 to 5 consecutive days with 4 to 5 legs per day (53%), successive

early wake-ups (41%), and night flights (18%).

These results are supported by the pilots’ responses

to the second question on fatigue causes during climb

and descent (Table II). Among the 8 items listed, sleep

deprivation remained the most important factor generating fatigue during climb and descent: 78% of LHF

pilots and 76% of SHF pilots considered that sleep

deprivation caused a “high” to “very high” impact on

fatigue. High workload and the density of verbal exchanges which characterize the climb and descent flight

phases yielded the second and third highest scores,

respectively. There was no significant difference between LHF and SHF, except that the latter assigned

significantly higher scores to the impact of high workload. Compared with captains, first officers reported

sleep loss and problems of coordination with other

crewmembers as producing significantly higher fatigue.

Table III shows the impact of five flight events on

fatigue. The scores attributed to these five items remained lower than that due to the lack of sleep (Table

II). The impact on fatigue was scored “high and very

high” by 50% or more of pilots for the following items:

dissension within crewmembers; necessity to perform

an originally unplanned additional leg; and compliance

with time constraints (only SHF).

Two significant differences were observed between

the two types of flights. The fatigue effect of the “necessity to perform an originally unplanned additional

leg” was significantly higher for LHF than for SHF,

while for “compliance with time constraints” the score

was significantly higher for SHF than for LHF.

There were no statistically significant differences associated with the gender of the pilots. Age, function,

and the duty time performed over the DW yielded the

following significant effects:

1. Pilots less than 35 yr of age attributed significantly

lower scores to “simultaneous actions,” “interrupTABLE II. CAUSES OF FATIGUE DURING CLIMB AND DESCENT.

Long-haul Flights Short-haul Flights

Significance

Mean Score

(SD)

High and Very

High Scores

Mean Score

(SD)

High and Very

High Scores

Significant workload 3.34 (0.92) 46.4% 3.53 (0.85) 53.8% *

Executing actions in a limited amount

of time 3.03 (0.86) 29.4% 3.17 (0.91) 34.6%

Simultaneous actions 2.97 (0.84) 23.1% 3.05 (0.85) 31.5%

Interruption during activities 2.76 (0.90) 19.6% 2.88 (0.95) 27.6%

Problem of coordination with the

other cockpit crewmembers 2.68 (1.04) 21.1% 2.79 (1.06) 26%

Density of verbal exchanges 3.17 (0.95) 38.9% 3.20 (1.03) 41.5%

Communicating in a foreign language 2.77 (0.96) 21.8% 2.69 (1.04) 19.4%

Lack of sleep 4.12 (0.86) 78% 4.10 (0.87) 76%

Ratings on a 5-point scale (1  no impact, 2  small impact, 3  medium impact, 4  high impact, 5  very high impact). Mean scores (SD)

and the percentages of pilots who scored “high and very high” are reported. *Significant differences between LHF and SHF mean scores;

Mann-Whitney U test, p  0.05.

TABLE III. IMPACT OF FLIGHT EVENTS ON AIRCREW FATIGUE.

Long-haul Flights Short-haul Flights

Significance

Mean Score

(SD)

High and Very

High Scores

Mean score

(SD)

High and Very

High Scores

Flight delay 3.01 (1.00) 32.4% 2.93 (0.97) 28.4

Difficult flight 3.05 (0.99) 34% 3.14 (1.03) 41.2

Dissension within crewmembers 3.40 (1.10) 51.5% 3.44 (1.11) 50%

Necessity of performing additional

leg not planned originally 3.91 (0.93) 72.4% 3.64 (1.03) 56% **

Compliance with time constraints 2.80 (1.02) 25.9 3.44 (1.06) 51% **

Ratings on 5-point scale (1  no impact, 2  small impact, 3  medium impact, 4  high impact, 5  very high impact). Mean scores (SD) and

the percentages of pilots who scored “high and very high” are reported. **Significant differences between LHF and SHF mean scores;

Mann-Whitney U test, p  0.001.

PILOT FATIGUE SURVEY—BOURGEOIS-BOUGRINE ET AL.

1074 Aviation, Space, and Environmental Medicine • Vol. 74, No. 10 • October 2003
tion during activities,” and “communicating in a

foreign language.”

2. First officers attributed significantly higher scores

to the “problems of coordination with the other

cockpit crewmembers,” “impact of lack of sleep,”

and “dissension among crewmembers.”

3. The level of fatigue related to the duty time over

the DW was positively correlated with the scores

attributed to the great majority of items: the impact of the different items on fatigue increased

with increasing duty time. This relationship was

not observed for only three of the items: “problems of coordination with the other cockpit crewmembers,” “density of verbal exchanges,” and

“dissension with other cockpit crewmembers.”

Manifestations of fatigue. The pilots reported 1,364

manifestations of fatigue for themselves and their cockpit crewmembers. The pilots’ responses were first classified according to their frequency, and then distributed

into three main categories: mental, verbal, and sleeploss related manifestations.

The item “reduction of attention and lack of concentration” was the most frequently reported manifestation of fatigue: 25% for LHF and 23% for SHF. For their

cockpit crewmembers, LHF pilots reported a “decrease

of social communication” in 31% of cases while SHF

pilots reported “small mistakes (calculation, interpretation)” in 26% of cases.

Among the three main categories, mental, verbal, and

sleep-loss related manifestations, 60% of LHF pilots and

49% of SHF pilots spontaneously reported manifestations related to sleep loss. For their cockpit crewmembers, pilots reported mainly mental manifestations (42%

and 53% for the LHF and SHF pilots, respectively). The

most frequent mental manifestations observed in other

crewmembers were “small mistakes (calculation, interpretation)” for SHF and “increases in response times”

for LHF (26% and 13% of manifestations of fatigue,

respectively).

In general, verbal manifestations, such as “a reduction of social communications and bad message reception (air traffic control, crewmembers, . . .),” were more

frequently reported for the other crewmembers than for

the pilots themselves: 49% of pilots reported this kind of

manifestation for the other crewmembers while only

22% of pilots did so for themselves.

When pilots were tired, all the flying tasks seemed to

be more difficult than usual (Table IV), especially supervisory activities, manual flying, and selecting and

entering data. The impact of fatigue on flying tasks did

not differ significantly between SHF and LHF except

that “utilization of aircraft automation” was more difficult for LHF. “Manual flying” was significantly more

difficult for first officers than for captains. Young pilots

(less than 35 yr) reported significant fatigue effects on

selecting and entering data, checklist, writing official

reports, and flight path monitoring.

Coping with fatigue. In the survey, 7% of pilots declared that they had no strategies to cope with fatigue, while 3% failed to respond to this question. The

remaining 90% cited a total of 1909 strategies which

could be classified into three main types: rest and

sleep management, activity management, and lifestyle. Rest and sleep management was the primary

strategy used to cope with fatigue in both flight categories before (79%) and after (88%) a duty sequence,

as well as during layover (74%). During flight, LHF

pilots reported that they took naps lasting 20 to 30

min (41%) while SHF pilots closed their eyes for 5

min (14%). The practice of napping before the rotation increased with age and was reported by 17%,

28%, and 36% of pilots less than 35, 35– 44, and more

than 44, respectively.

DISCUSSION

The causes of pilots’ fatigue are primarily related to

sleep loss for both LHF and SHF. Pilots reported that

night flights and jet lag were the most important factors

that generated fatigue in LHF; for example, two successive night flights to Paris-New York-Paris in 48 h with

a short layover of about 22 h. In this case, the sleep

taken soon after arrival corresponds to biological day.

The poor quality and quantity of this sleep, together

with the long period of wakefulness before departure,

increased fatigue during the nocturnal return flight. In

SHF, multi-leg flights and early wake-ups increased

fatigue in SHF. These results confirm those observed by

Nicholson et al. (12) for LHF, and Gander et al. (6) for

SHF.

In addition, the results indicate that time constraints,

high numbers of legs per day, and consecutive work

days seemed to increase fatigue in SHF. The effect on

fatigue of the necessity to perform an originally unplanned additional leg was significantly higher for LHF

than for SHF probably because of the previous long

duty time. Alternatively, it may be that SHF pilots are

more familiar with this type of request.

When considering themselves, pilots cited the manifestations of fatigue caused by sleep deprivation as a

reduction in alertness and attention, and a lack of concentration. However, for their cockpit crewmembers,

they reported mental manifestations (increased response times, small mistakes) and verbal manifestations

(reduction of social communications, bad message reTABLE IV. MEAN (SD) IMPACT OF FATIGUE

ON FLYING TASKS.

LHF SHF Significance

Monitoring 62.9 (13.1) 63.5 (13.0)

Flight path monitoring 68.0 (13.1) 67.6 (12.2)

Manual flying 72.0 (14.8) 74.7 (14.7)

Utilization of aircraft

automation 66.4 (14.9) 61.6 (15.3) **

Communication 64.8 (13.8) 64.0 (13.7)

Crew resources management 66.4 (13.8) 66.5 (14.0)

Check-list 58.3 (11.8) 57.9 (12.8)

Briefing 60.5 (12.2) 61.8 (13.3)

Monitoring supervisory

activities 75.3 (13.3) 75.8 (11.9)

Selecting and entering data 71.6 (13.8) 69.3 (12.7)

Writing official reports 67.6 (16.2) 6.7 (17.0)

Analogue scale used: 0  less difficult than usual, 50  as usual,

100  more difficult than usual. **Significant differences between

LHF and SHF, Mann-Whitney U-test, p  0.001.

PILOT FATIGUE SURVEY—BOURGEOIS-BOUGRINE ET AL.

Aviation, Space, and Environmental Medicine • Vol. 74, No. 10 • October 2003 1075
ception). These results suggest that pilots may not really be aware of the effects of fatigue on themselves in

terms of the quality of their flight task performance.

The increase in response times for LHF may be due to

pilots’ ability to manage their activities during the long

cruise phase, whereas for SHF, omissions and small mistakes were probably related to time pressure and a high

workload during the short, multi-leg flights. When crewmembers are tired, supervisory or monitoring activities

become more difficult than usual. This result confirms the

finding that sleep loss and fatigue affect the less demanding tasks (type 1) (4). Likewise, Lyman and Orlady (10)

have shown that in the majority of ASRS fatigue-related

incidents, there is a decrement in monitoring performance

(e.g., activities that involve awareness of the actual and

desired state and position of the airplane).

Rest and sleep management is the primary strategy

used to cope with fatigue in both flight categories before (79%) and after (88%) a duty sequence, as well as

during layover (74%). The practice of napping before

the rotation increases with age.

Younger pilots seemed better able to resist fatigue

than older ones: pilots less than 35 yr of age attributed

significantly lower scores to the fatigue impact of “simultaneous actions,” “interruption during activities,”

and “communicating in foreign languages.” In addition, for these younger pilots, fatigue had significantly

less impact on flying tasks “selecting and entering

data,” “check-list,” “writing official reports,” and

“flight path monitoring.” It is well known that younger

drivers are better able to resist fatigue (7, 8, 14). Hamelin found that drivers over the age of 30 have lower

strength resources, which limits their ability to compensate for fatigue effects (7). However, younger drivers

cause proportionately more accidents related to sleepiness than older ones because they drive more at night

(8).

The analysis confirmed that fatigue increased significantly with cumulative duty time during the preceding

DW. For LHF, nocturnal duty was the most important

predictor of fatigue. Nevertheless, the regression model

failed to explain the majority of the variability in fatigue. There are probably two explanations for this

result. First, the effect of duty time may be veiled by the

many other factors related to the duty sequence, such as

the early wake-ups, jet-lag, multiple legs per day, the

number of consecutive days of work, the high workload, and time constraints. Second, the ratings of fatigue

were made at different times of day and may have been

influenced by circadian variations in fatigue, prior sleep

loss, and time since sleep. For instance, pilots with

relatively low cumulative duty times may rate their

level of fatigue as high if they are suffering from sleep

loss, or if they make the rating during the night. The

predictive model of fatigue showed that duty time may

help to predict fatigue but that it cannot be considered,

or manipulated, independently from the other factors

that control fatigue. A further survey is currently being

prepared to extend these preliminary results and to

improve the predictive model by taking into account all

the features of work schedules. We also plan to examine

the other factors that can affect sleep such as the stress

due to personal or professional problems, health, and

lifestyle.

The outcomes of fatigue reported by pilots, such as

the reduction of alertness and lack of concentration, are

not specific to sleep loss and are difficult to quantify in

analyzing accidents or incidents. However, the main

causal factors of pilots’ fatigue could be easily assessed;

specifically, preceding work schedules could be analyzed to evaluate circadian disturbances caused by

night flights or jet lag, sleep loss due to morning or

night flights, and cumulative duty time.

We applied this approach to an investigation of a

serious incident that occurred on a final approach to

Paris-Orly Airport in 1997 to evaluate whether or not

the pilots were sleep-deprived (5). Analysis of their

work schedules for the prior 30 d indicated no circadian

disturbances, but a cumulative sleep loss over the last

7 d prior to the incident due to “short nights off”

(finishing late and starting early). Interviews with the

pilots confirmed that they felt tired before the incident.

CONCLUSIONS

The fatigue reported by pilots reflected the effects of

their work schedules: night flights, jet lag, and successive early wake-ups. For SHF, time pressure, number of

legs per day, and consecutive days on duty contributed

to increased fatigue. The results of this study emphasize

the need to consider chronobiology in the development

of aircrew scheduling rules, as well as flight and duty

time limitations to allow for the additional fatigue effects of multi-leg flights and work constraints in SHF.

Finally, pilots should be made aware that the effects of

fatigue include not only the self-reported reduction of

alertness and attention, and lack of concentration, but

also produces in them the signs that they observed in

other crewmembers, including increased response

times, small mistakes, a reduction of social communications, and bad air traffic control message reception.

ACKNOWLEDGMENTS

We would like to thank the DGAC (Direction Ge ́ne ́rale de

l’Aviation Civile) for the financial support of this study, the pilots for

their participation and the following airlines for their cooperation: Air

France, Air Liberte ́, AOM, Corsair, Postale, and Aeropostale.

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